1. Field of the Invention
The present invention is related to methods for improving image sticking of liquid crystal displays (LCDs), and more particularly, to a method of utilizing a residual voltage to improve the image sticking of the LCD.
2. Description of the Prior Art
FIG. 1 is a diagram of a liquid crystal display (LCD) according to the prior art. The LCD 100 is formed of two glass substrates: an upper layer UL and a lower layer LL. A liquid crystal layer LCL is infused between the two glass substrates. The liquid crystal layer comprises liquid crystals LC. A top of the glass substrate LL comprises a plurality of data lines and a plurality of scan lines, and a plurality of pixel regions are formed by intersections of the plurality of scanlines and the plurality of data lines. However, the structure described above is not ideal in practice, thus the liquid crystal layer LCL is not only filled with the liquid crystals LC, but also contains impurities P. As shown, the impurities P may be positively charged or negatively charged.
FIG. 2 is a diagram of the LCD of the prior art when displaying an image. As shown, when displaying the image, a voltage difference is generated across the glass substrates UL and LL to cause the liquid crystals LC to turn. In other words, an electric field E is established across the glass substrates UL and LL. As the liquid crystals LC turn, the impurities P will also move with the electric field according to their individual electric charges.
FIG. 3 is a diagram of the LCD of the prior art after having displayed the image for a period of time. As shown, after displaying the image for the period of time, the electric field E established across the glass substrates UL and LL makes shifting of the impurities P more thorough. Thus, the impurities P charged positively congregate on one side, whereas the impurities P charged negatively congregate on another side. In this situation, because the impurities P shift slowly, after the electric field E disappears, the impurities P will not immediately return to the original state. Thus, the impurities P will generate another electric field in the liquid crystal layer LCL, such that the liquid crystals LC, which were supposed to return to their predetermined positions, are affected, such that they are unable to return to their predetermined positions. In other words, if the originally preset electric field is E1, the impurities P congregate to generate an electric field E2. Under perfect conditions, the electric field that the liquid crystals LC experience is E1, and the liquid crystals LC are able to return to their predetermined positions according to the electric field E1. However, due to the effect of the electric field E2 caused by the impurities P, the electric field experienced by the liquid crystals LC becomes E1+E2 in practice. Thus, the liquid crystals LC are unable to return to predetermined positions easily, causing an image sticking phenomenon.
FIG. 4 is a second diagram of the image after displaying the image for a period of time with a conventional LCD. The direction of the shift in the impurities P is not only affected by the electric field E, but also by the turning of the liquid crystals LC. As shown in FIG. 4, because the liquid crystals are slanted slightly by the electric field E, the impurities P will not only shift in the vertical direction, but will also shift in the horizontal direction. The movement of the impurities P will result in trapping of the impurities P between a certain few pixels of the LCD 100 (trapping is related to the image displayed), such that the influence of the impurities P on pixels where more of the impurities P are trapped is greater, and the influence of the impurities P on pixels where fewer of the impurities P are trapped is less. When this happens, the electric field experienced by the liquid crystals of the pixels with more trapped impurities P will have a marked difference from the electric field experienced by the liquid crystals of the pixels with fewer trapped impurities P. This causes a non-uniform condition when displaying the image, and is also known as line image sticking.